1. Field of the Invention
This invention relates to a novel pressure-sensitive transfer member which can give sufficiently sharp transferred images even at a low impact energy.
2. Related Background Art
There have been heretofore known pressure-sensitive transfer members for transfer recording letters, etc. on a member to be attached such as paper, etc. by utilizing an impact energy by a type bar or a print ball, etc. The impact printer utilizing a pressure-sensitive transfer material, while it is capable of higher speed printing as compared with an impact printer of the pressure-sensitive or current-passage system utilizing heat energy, a great impact energy is required during printing on the other hand, thus involving the drawback of great noise during printing operation.
In recent years, with the progress of development of information instruments, there is increasingly a demand for low noise in printing working, and an impact printer utilizing daisy wheel has been widely employed in place of the type bar or print ball as described above. However, even in an impact printer utilizing daisy wheel, an impact energy of about 10 mJ/mm.sup.2 on an average is required during printing, and the noise accompanied therewith has not been reduced to the extent as in the case of the pressure-sensitive or current-passage system impact printer under the present situation.
Under such circumstances, recently in printing by an impact printer, for the purpose of making the noise further lower, during printing by means of the above impact printer utilizing the daisy wheel, it has been proposed to reduce the impact energy. However, when printing is effected with reduced impact energy by use of the pressure-sensitive member of the prior art, transfer badness such as letter defect or shortage of sharpness, etc. will generally occur.
On the other hand, it has been also practiced to attempt reduction of impact energy after weakening the adhesive force between the substrate and the ink layer constituting the pressure-sensitive transfer member, but such a pressure sensitive member will suffer from the back transfer phenomenon (or blocking) in which the ink layer is plastered onto the back surface of the substrate when it is wound up in a ribbon for use as the ink ribbon.
Thus, up to date, the problems antagonistic to each other of transfer performance and the back transfer phenomenon concerning the adhesiveness between the substrate and the ink layer of the pressure-sensitive transfer member remain to be solved under the present situation.
Whereas, the substrate of the pressure-sensitive transfer member for ink ribbon for impact printer, etc. as described above is generally made a film, and the ink layer provided thereon is composed mainly of a resin capable of forming a coating and a low volatile oil which will not plasticize the resin. Concerning the printing mechanism of such pressure-sensitive transfer member, much remain still to be clarified, but generally speaking, by giving an impact energy overcoming the adhesive force between the substrate and the ink layer to the ink ribbon during printing, agglomeration breaking of the oil existing in spots in the ink occurs first, followed subsequently by breaking of the resin existing in porous film in the ink layer simultaneously with migration of the oil onto the ink layer surface, whereby adhesion of the ink layer, namely printing, onto the member to be attached is considered to occur.
Accordingly, in order to realize low noise of the impact printer by use of such a pressure-sensitive transfer material without causing the problems of transfer badness such as letter defect, etc. or back transfer phenomenon, it is necessary to prevent letter defect or lowering in sharpness by making smaller the adhesive force between the substrate and the ink layer to the extent corresponding to reduction in impact energy, and at the same time maintain the adhesive force to the extent which will not cause the back transfer phenomenon as a problem antagonistic thereto, namely to consider the balance of the adhesive force between the substrate and the ink layer.
As a factor which may be considered to have great influence on the adhesive force, there may be considered the degree of compatibility between the resin and oil components contained in the layer. If the degree of compatibility is low, tackiness between the resin and oil is weakened, whereby the adhesive force between the substrate and the ink layer will be consequently weakened. In the pressure-sensitive transfer member for light hitting of the prior art, only an oily substance substantially incompatible with the resin component has been used as the oil. For this reason, although the adhesive force between the substrate and the ink layer could be weakened corresponding to reduction in impact energy, the back transfer phenomenon could not be fundamentally cancelled.